1. Field of the Invention
The present invention pertains to apparatus for gripping and manipulating tubular members, such as pipe members. More particularly, the present invention relates to apparatus for manipulating pipe members into and out of wells, and finds particular application in workover rigs and snubbing units.
2. Description of Prior Art
In the drilling and operation of wells, it is frequently necessary to insert or remove strings of pipe into or out of wells. Such pipe manipulation often takes place while the well is under high fluid pressure. Under such conditions devices have been employed for forcing the tubing through suitable stuffing boxes, such as are formed by blowout preventers and the like, to maintain control of the pipe string as it is being run into or out of the well. Such devices are commonly referred to as "snubbers".
While snubbers are usually designed primarily for forcing the pipe string down into a well against downhole fluid pressure resisting such motion by the pipe string, similar devices are known for applying upward forces to support part or all of the weight of a tubing string in the case of low pressure or dead wells, as well as to raise the tubing string from the well. Also, where it is desired to eliminate the need for a separate rotary drive device to impart torque to pipe members, or even rotate the entire pipe string, a pipe gripping head, such as a snubber head, may be mounted to be driven rotationally while gripping the pipe.
Typical snubbers and like devices are constructed with a pair of heads equipped with slips for gripping the pipe members. One head, such as the lower head, is usually held stationary relative to the well while the other head, known as the traveling head, is selectively manipulated back and forth above the stationary head. By appropriate gripping and releasing of the pipe string by each of the heads, pipe may be advanced into the well or removed therefrom. One or the other of the heads may be rotatable to rotate the pipe gripped thereby while the other head may lock pipe gripped thereby against rotation.
U.S. Pat. No. 3,722,603 discloses a fluid pressure-operated snubber device including two snubbing members, or heads, equipped with pipe-gripping wedges and cam actuated shoes for applying torque to pipe. One of the snubbing members is stationary and one is rotatable and vertically reciprocable.
In the apparatus disclosed in U.S. Pat. No. 3,742,563, a gripping assembly includes a set of slips and a set of wedges by which the slips may be wedged into gripping engagement with pipe. Cam means are provided to cooperate with the wedges to move the slips into tighter engagement with the pipe upon rotation of the pipe. U.S. Pat. No. Re. 25,860 a reissue of U.S. Pat. No. 3,096,075 and U.S. Pat. Nos. 3,760,469 and 3,748,702 further disclose means whereby slip segments may be driven generally radially into gripping engagement with pipe, and grip the pipe for application of forces thereto in either axial direction.
U.S. Pat. Nos. 3,776,320; 3,915,244 and 3,964,552 disclose elevator assemblies including slips which are generally radially movable by camming mechanisms to apply torque to pipe.
It is advantageous to effect gripping engagement between slips and pipe to be manipulated without sliding motion between the slips and the pipe to minimize wear on the slips. Further, it is advantageous to effect such gripping engagement to impart forces to the pipe parallel to the longitudinal axis of the pipe in both senses, as well as to impart torque to the pipe about that axis, with the same set of slips, and without the necessity of disengaging and reorienting the slips to effect the different forces.